Method of heating the interior of an enclosure



July 3, 1962 R. CHENAULT 3,042,557

METHOD OF HEATING THE INTERIOR OF AN ENCLOSURE Filed April 16, 1959 IN VEN TOR.

ROY I. CHE/VAULT ATT'ORNEY 3,042,557 Patented July 3, 1962 3,042,557METHOD OF HEATING THE INTERIOR OF AN ENCLOSURE Roy L. Chenault, Seneca,Pa., assignor to United States Steel Corporation, a corporation of NewJersey Filed Apr. 16, 1959, Ser. No. 806,946 3 Claims. (Cl. 148-144)This invention relates to an improved method of heating the interior ofan enclosure.

An object of the invention is to provide a heating method whichmomentarily develops an extremely high temperature within an enclosure,useful for example for casehardening the inside surface of a metal tube.

A further object is to provide an improved casehardening methodapplicable to metal tubes in which the inside surface of the tube isheated momentarily above its critical temperature and immediatelyquenched by conduction of heat to other regions of the tube.

A more specific object is to provide an improved casehardening method inwhich a suitable fuel is charged into a tube along with sufiicientoxygen for complete combustion, the ends of the tube are sealed, and thecharge ignited, whereby the inside surface is heated momentarily aboveits critical temperature and immediately quenched by conduction of heataway from this surface.

In the drawing:

FIGURE 1 is a somewhat diagrammatic longitudinal sectional view of atube prepared for heating in accordance with my method; and

FIGURE 2 is a similar view showing a modification.

FlGURE 1 shows a metal tube which contains a finely divided solid fuelcharge 1'2, for example aluminum or magnesium in powder or wool form.Alternatively I can substitute a gaseous fuel, such as propane orbutane, or other recently developed high energy solid, liquid or gaseousfuels. Plugs 13 and 14 are fitted into the left and right endsrespectively of the tube. Plug 13 contains a bore 15 into which isthreaded a pipe 16 containing a valve 17. The tube is evacuated andcharged through pipe 16 with a calculated quantity of oxygen forcomplete combustion of the fuel, after which valve 17 is closed. if agaseous fuel is used, it is also introduced through pipe 16. Plug 14contains a bore 18 and counterbore 19. A cap 20 is threadedly engagedwith plug 14 and covers the countcrbore. The cap contains a bore 21 intowhich is fitted an electrically insulating seal 22, an electrode 23 andan ignition means 24, such as a conventional photographic flash bulbillustrated for igniting solid fuels. The cap and electrode areconnected to a suitable current source indicated at 25 for firing theflash bulb.

When the fuel charge 12 is in powder form, the tube is mounted in aconventional lathe or equivalent mechanism for spinning it on itslongitudinal axis and thus distributing the powder uniformly over theinside surface by centrifugal force. In this event the end of bore 21contains an intermediate igniter 26 preferably of ahuninum or magnesiumwool. When the flash bulb 24 fires, it ignites the intermediate igniter,which in turn ignites the fuel charge. When the fuel charge is aluminumor magnesium wool, it is not necessary to rotate the tube and theintermediate igniter can be omitted, since the fuel charge is exposeddirectly to the flash bulb. Another possibility with a powdered fuelcharge is to direct the bore 21 obliquely at the charge to expose thecharge directly to the flash bulb and again omit the intermediateigniter. When a gaseous fuel is used, the ignition means 24 can be aconventional spark plug. The purpose of mounting the ignition means in aseparate chamber provided by the counterbo-re 1 and cap 20 is thatotherwise the high temperature developed when the fuel burns tends tofuse the base and seal. Thus considerable trouble would be encounteredin reconditioning the equipment for further use.

FIGURE 2 shows a modification in which an auxiliary chamber 27 isconnected to pipe 16 at the left end of tube 10. This chamber cancontain part of the oxygen supply and thus lower the pressure within thetube 16 while maintaining the necessary quantity of oxygen. An auxiliaryoxygen supply can also serve as a means to regulate the rate of burningand thus control both maximum temperature and maximum pressure obtainedfor a given fuel charge representing a given amount of energy to bedissipated.

The range of aluminum or magnesium for pnactical use as fuel incasehardening the inside of a steel tube is about 10 to grams per squarefoot of surface. The lower limit of the fuel charge is determined by theminimum which produces a useful hardness increase and may involve anextremely thin case. The upper limit of the charge is determined by themaximum which does not cause burning or fusing of the tube surface. Theoxygen charged preferably is substantially the quantity required forcomplete combustion of the fuel without appreciable excess. The casecharacteristics can be varied by varying the size and shape of powderedfuel particles, as well as the quantity. In general coarser mesh powderburns more slowly than finer mesh, and granular particles more slowlythan flaky. The tube can be quenched in water or oil if more rapidcooling is needed.

My instantaneous heating method also produces momentary high pressureswithin an enclosure at the same instant the temperature is high. Suchpressure may also have a beneficial effect along with the temperature.An example is when my heating method is used in the coating of a surfacewith high melting point enamels, plastics or the like. Such coatings areused to make porous materials impermeable, and the application ofpressure along with temperature tends to force the sealing material intothe pores of the surface to produce a better bond and a more permanentcoating. My method may also be utilized to induce chemical reactionsthat occur under the simultaneous application of high pressure and hightemperature.

Example I As a specific example of my method, I selected a tube ofA.I.-S.I. 1045 steel 10 inches long, 1 /2. inches inside diameter, andhaving an initial hardness of 20 to 25 Reel- Well C. I introduced a fuelcharge of 4 grams of minus 60 mesh powdered aluminum along with oxygenat a pressure of p.s.i.g. at 75 F. I prepared the tube as shown inFIGURE 1, spun it in a lathe to distribute the fuel charge, and firedthe ignition means. Subsequently I found that the inner surface of thetube had acquired areas hardened to about 55 to 65 Rockwell C.

Example 11 As a further example, I introduced to a similar tube a fuelcharge of 8 grams of minus 60 mesh powdered magnesium along with oxygenat a pressure of p.s.i.g. at 75 F. I prepared the tube, spun it andfired the ignition means as in the first example. Subsequently I foundthat the inner surface had acquired a case approximately & inch deepwith a hardness of about 55 to 65 Rockwell C. I found magnesiumpreferable to aluminum for the reason that I was able to attain a moreuniform case with magnesium. I attribute this result to the highermelting point of MgO (5072 F.) compared with Al O (3722 F). The latterforms droplets which tend to create hot spots when they solidify. Thischaracteristic is not observed with MgO, presumably because of itshigher melting point.

From the foregoing description it is seen that my invention affords asimple and effective method of flash-heating the interior of anenclosure. The method is especially If: applicable to casehardening asdescribed in the examples, although it may have other applications.

While I have shown and described certain preferred embodiments of myinvention, it is apparent that other modifications may arise. Therefore,I do not wish to be limited to the disclosure set forth but only by thescope of the appended claims.

I claim:

1. A method of casehardening the inside surface of a metal tubecomprising introducing to the tube a fuel charge along with sufficientoxygen for complete combustion of the fuel, sealing the ends of thetube, igniting the charge to heat the inside surface momentarily aboveits critical temperature, and quenching the inside surface by conductionof heat therefrom.

2. A method of casehardening the inside surface of a steel tubecomprising introducing to the tube a finely divided solid fuel charge ofthe group consisting of aluminum, magnesium and combinations thereof inthe amount of to 75 grams of fuel per square foot of surface, along withsuflicient oxygen for complete combustion of the fuel, sealing the endsof the tube, igniting the charge to heat the inside surface momentarilyabove its critical temperature, and quenching the inside surface byconduction of heat therefrom.

3. A method of casehardening the inside surface of a steel tubecomprising introducing to the tube a finely divided powdered solid fuelcharge of the group consisting of aluminum, magnesium and combinationsthereof in the amount of 10 to grams of fuel per square foot of surface,along with sufficient oxygen for complete combustion of the fuel,sealing the ends of the tube, spinning the tube on its longitudinal axisto distribute the fuel charge over the inside surface, igniting thecharge to heat the inside surface momentarily above its criticaltemperature, and quenching the inside surface by conduction of heattherefrom.

References Cited in the file of this patent UNITED STATES PATENTS829,117 Maxim Aug. 21, 1906 2,318,145 Emery et al May 4, 1943 2,448,203Africano Aug. 31, 1948 2,464,179 Hickman et al Mar. 8, 1949 2,596,981Ohennault et a1 May 20, 1952 2,669,511 Whitney Feb. 16, 1954 OTHERREFERENCES Johnson: Metal Working and Heat-Treatment Manual, Volume III,Lib. Call No. TS 205 vc; pages 89, 106, 107, and 121, dated 1948.

1. A METHOD OF CASEHARDENING THE INSIDE SURFACE OF A METAL TUBECOMPRISING INTRODUCING TO THE TUBE A FUEL CHARGE ALONG WITH SUFFICIENTOXYGEN FOR COMPLETE COMBUSTION OF THE FUEL, SEALING THE ENDS OF THETUBE, IGNITING THE CHARGE TO HEAT THE INSIDE SURFACE MOMENTARILY ABOVEITS CRITIAL TEMPERATURE, AND QUENCHING THE INSIDE SURFACE BY CONDUCTIONOF HEAT THEREFROM.